This invention relates in general to volumetric 3D (V3D) display systems based on a moving display surface. Specifically, this invention relates to V3D display systems based on a rotary reciprocating display surface. More specifically, this invention relates to V3D systems with slim and. compact system layout and package, smooth and quiet motion mechanisms and image display method. Conversion among different display modes and modular system design are also considered in the compact and slimness design.
One category of V3D display creates images by projecting successive picture frames onto a moving 2D screen, or by displaying successive picture frames on a moving 2D display surface, such as a light-emitting 2D display panel. Due to the after-image effect of human eye, the set of spatially distributed picture frames displayed on the moving screen form V3D images.
Tsao U.S. Pat. No. 6,765,566 (FIG. 20) describes a system with a screen that reciprocates by a rotary motion, as illustrated in FIG. 1. In principle, this is to revolve the screen 2031 about an axis 2000 and sweep the screen across a volume 2040 while keeping the screen surface always facing a fixed direction. For convenience, this is called “Rotary Reciprocating mechanism”. The advantage of Rotary Reciprocating mechanism is that a motion equivalent to reciprocation can be generated by smooth rotary motion without the need of linear bearings, which in general have higher cost, higher noise and shorter life than rotary bearings. Iwahara Japan patent application publication S56-123533, incorporated herein by reference, describes a similar motion using different mechanical details.
In practical operation, Iwahara's system has the following problems: (according to his drawing)
(1) The screen 1 is elevated above the level of the moving shafts (3, 4 of Iwahara) by a framework (2 of Iwahara). Therefore, the mass center of the screen+framework assembly is also elevated above the level of the moving shafts. In actual rotation, this can create a torque, which in turn induces forces exerted to the rotary arms in opposite directions, as illustrated in FIG. 2. This affects the smoothness of the rotation, especially at “mid-crossing” position. “Mid-crossing” is when the moving centerline (moving CL) passes the plane defined by the two main centerlines (main CL). (A main centerline is the line connecting the rotating center of the two arms on the same side. A moving centerline is the line connecting the centers of the two moving shafts on the same side.) At mid-crossing, positions of the arms and the screen-framework assembly are not definitely fixed in terms of kinetics. The only mechanism to hold the components in position is the timing belt (18 of Iwahara) and gears (17, 19 of Iwahara). However, a flexible timing belt has unavoidable elasticity. At or near mid-crossing, the two moving shafts, suddenly loosing kinetic constraint, are pushed by the torque mentioned above to opposite directions, resulting in a “jump” of the screen-framework and associated noise. This has been observed in our tests.
(2) Iwahara's screen-framework assembly appears to be a rigid structure. Therefore, the center distance between the bearing holes on the frame must match the center distance between the two moving shafts (3, 4 of Iwahara) (and between the main shafts (5, 6 of Iwahara)) to a very high precision. Although this is not impossible, for machine of certain size, such precise tolerance can be costly, because errors become larger by leverage and accumulation on machines of larger size.
(3) Iwahara's system has a timing belt-gear mechanism on one side only. In principle, the two moving shafts (3, 4) can be rigidly connected to the arms on both sides and make the whole moving portion a rigid body. But in practice, especially when the machine has certain size, the deformation of materials and the clearance in bearings on the main shafts may not guarantee the synchronization of motion on both sides. Coupled with problems from (1) and (2), the actual motion cannot be smooth and quiet.
(4) The two long moving shafts (3, 4 or Iwahara) take significant space when they rotate. This is undesirable in making a compact system.
Therefore, a purpose of this invention is to develop mechanisms for a Rotary Reciprocating display surface for volumetric 3D display purpose to achieve smooth and quiet motion. The display surface, either a projection screen or a display panel, needs to be well supported against significant deformation and stress while the mechanism is in motion. And the system needs to be compact and cost-effective in order to become a viable product.
Another issue in designing a slim portable system is the size and structure of the mechanical mechanism for driving the screen motion. The rotary arms, the driving components (gears and belts) and the housings that accommodate the axes of the rotary arms require certain size (thickness). For example, FIG. 3 illustrates a sectional view of a example driving mechanism. The shaft-gear-belt mechanisms of the rotary arms are placed on both side of the screen 2032, because the projection beam 399 must pass from under the screen along projection centerline 303. The shaft-gear-belt housing has a two-wall structure, with the gear in between, so that the shaft can be held at definite position. On both sides, these structures and components occupy some space. If the moving screen size is large, then the space occupied by the mechanism is comparably insignificant. However, if the screen size is small, such as in the case of a hand-held system, then the space occupied by the mechanism becomes comparably significant. This is not desirable for a hand-held system.
Another issue is to project images to the screen and keep the image in focus. Tsao U.S. Pat. No. 7,933,056 describes a rapid focusing system using a moving thin wedge prism to compensate projection focal distance. In a slim portable system with multiple display modes, such a rapid focusing system needs to be incorporated into the display system without affecting the functionality of multi-mode conversion, while keeping the whole system slim.
Tsao U.S. patent application Ser. No. 13/271,701 describes a volumetric 3D display system capable of multiple display modes, including 2D front projection, 2D rear projection, and as3D display. Such a multi-functional projection system has potential commercial attractiveness. Therefore, it is also preferred that the design of layout for slimness and compactness accommodates the restrictions imposed from functional requirements for multiple display modes. The mechanical and opto-mechanical parts of the system must be able to be converted among different display modes easily and also be able to be positioned to a slim and compact status when needed.
The purpose of this invention further includes designs of electronic systems that are convertible for different display modes.